In recent years, the use of wireless energy transfer or wireless power transmission has been used to transfer electrical energy from a power transmitter (such as a source) to a receiver without the use of interconnecting wires. Wireless energy transfer is useful in cases where instantaneous or continuous energy transfer is needed where interconnecting wires are inconvenient or hazardous. Typically, wireless energy transfer involves the use of antennas which are used to transmit and/or receive power and data using time-varying currents, such as alternating currents. Such systems are generally referred to as inductively coupled systems.
The efficiency of energy transfer between two devices in an inductively coupled system is based on the quality factor of the antenna in transmitter (Q1), the quality factor of the antenna in the receiver (Q2), and the coupling coefficient between the two antennas (κ). The efficiency of the energy transfer varies according to the following relationship:eff∝κ2·Q1Q2 
The quality factor represents the rate of energy loss relative to the stored energy of the antenna. A higher quality factor indicates a lower rate of energy loss relative to the stored energy of the antenna. Conversely, a lower quality factor indicates a higher rate of energy loss relative to the stored energy of the antenna. The coupling coefficient expresses the degree of coupling that exists between two antennas. The value of the coupling coefficient may be based on the proximity of the antennas, the orientation of each antenna relative to the other antenna, and the environment in which the antennas are located. A higher coupling coefficient may be achieved by placing the antennas closer to one another, by orientating each antenna such that electromagnetic fields generated by the antenna are aligned, or removing environmental elements that reduce the strength of the generated electromagnetic fields.
Although the quality factor may increase the efficiency of an inductively coupled system, the quality factor inversely affects the bandwidth that is available to transmit data. Specifically, the bandwidth available to transmit data (BW) is inversely proportional to the quality factor of an antenna and varies according to the following relationship:
  BW  ∝      1    Q  
As a result, a higher quality factor reduces the available bandwidth for data transmission. Given the mathematical relationship between the bandwidth and quality factor, data-intensive systems that require significant bandwidth will require that the quality factors of the transmitting and receiving antennas be decreased. The low quality factor of the antennas in these systems requires a high coupling coefficient in order to increase the efficiency of energy transfer between the transmitter and the receiver in the system. However, often times, it may not be possible to increase the coupling coefficient due to the various environmental constraints.
Recently, implantable tissue stimulation systems have been developed to provide electrical stimulation for the treatment and management of chronic intractable pain, heart arrhythmia, and other medical conditions in which stimulation may be beneficial. Generally, these systems include an implantable controller device and at least one stimulating electrode for providing electrical stimulation to tissue. The implantable controller device (such as an implantable pulse generator) controls the stimulation that is provided to the tissue. The implantable controller device may control the stimulation by providing continuous stimulation control signals to the stimulating electrodes that control the pulse amplitude, pulse width and frequency, and pulse pattern applied by the stimulating electrode. Wire leads originate from the implantable controller device and terminate in stimulating electrodes at the stimulation site. One disadvantage of current tissue stimulation systems is the formation of scar tissue around the lead wires leading to the breakage and/or migration of the lead wires due to stress and strain caused by body movement. An improvement over these existing systems would be to remove the wires and design a system in which the implantable controller device could wirelessly provide power and stimulation control signals to the stimulating electrodes.
Currently available implantable tissue simulation systems also require high-data transfer rates because the implantable controller device controls the stimulation by providing continuous signals to the stimulating electrodes. As noted above, in wireless communications, data intensive systems require substantial bandwidth. In designing such systems, the quality factors of the transmitting and receiving antennas must be reduced in order to achieve the necessary bandwidth required for data transmission. Thus, in order to achieve high efficiency systems with a low quality factor; it is necessary to have a high coupling coefficient between the transmitter and the receiver in the system. However, it may not be possible to achieve a high coupling coefficient in certain environments.
Thus, there currently exists a need for an improved system and method for energy transfer between two more or more devices in a system via high quality factor resonant inductive coupling.